Release coating

ABSTRACT

Described herein is the use of a modified PET in combination with a vinyl addition silicone water-based release coating to provide performance equivalent to the silicone by itself at a lower cost than the silicone by itself and resulting in a release backing paper that can be repulped and recycled in conventional recycled paper mills avoiding the additional cost of sending the scrap paper to landfill.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 13/252,983, filed Oct. 4, 2011, which claims the benefit ofU.S. Provisional Application No. 61/390,088 filed on Oct. 5, 2010, thecontents of which are hereby incorporated by reference herein in theirentirety for all purposes.

BACKGROUND OF THE INVENTION

Silicone-based release coatings are useful in applications whererelatively non-adhesive surfaces are required. For example, pressuresensitive adhesive labels may have a backing sheet that has appliedthereto a silicone-based coating to retain the labels without affectingthe adhesive properties of the labels.

For example, for the preparation of pressure sensitive adhesive labels,a paper layer such as glassine, wood free paper or kraft paper, iscoated with a silicone-based film. The silicone film is then adhered toby the adhesive material of the label stock. The silicone-based releasefilm allows the adhesive material of the label stock to be easilyremoved and for the label stock to still retain its adhesivecharacteristics.

The typical methods for providing release papers for adhesives is basedon three chemistries: silicone, chrome complex and polyethylene (PE).None of these treatments allow the backing paper to be recycled.

In addition, there are three different silicone types: solvent based,solventless or water-based. Solvent based technology requires a solventrecovery system so that the solvent does not escape to the environmentcausing pollution and to make the process economical. Solventlesstechnology is expensive and the catalyst can be easily inactivated byminor contaminants. Solvent-based and solventless technologies bothproduce a backing paper which is not repulpable or recyclable.Water-based silicone technology can provide performance for a broadrange of adhesives, but the resulting backing paper is not repulpable orrecyclable. The chrome complexes, some of which can be considered ashaving non-objection status from the FDA for food contact, stillrepresent a potential environmental hazard because of their chromiumcontent.

PE is not recyclable and like the chrome complex, does not provideperformance to a broad range of adhesives, especially the moreaggressive types.

Published PCT Application WO2008/019953 teaches a polyorganosiloxanebased release coating composition which can be used to coat polyesterfilms.

Published PCT Application WO 2010/012787 teaches a liquid siliconecomposition for coating a number of substrates, including polyethyleneterephthalate type polymer films.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided arelease coating for a pressure sensitive adhesive product comprising:

60-90% polyethylene terephthalate modified by the addition of carboxylfunctional fatty acids and 10-40% water dispersible or emulsifiablesilicone.

According to a second aspect of the invention, there is provided amethod of applying a release coating onto a pressure sensitive adhesiveproduct comprising:

mixing 10-40% water dispersible or emulsifiable silicone with 60-90%polyethylene terephthalate modified by the addition of carboxylfunctional fatty acids in the presence of a suitable catalyst, therebyproducing a release coating; and

applying the release coating to a suitable support.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. Although many methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described. All publications mentioned hereunderare incorporated herein by reference.

Described herein is the use of a modified PET in combination with avinyl addition silicone water-based release coating to provideperformance equivalent to silicone coatings at a lower cost than thesilicone by itself and resulting in a release backing paper that can berepulped and recycled in conventional recycled paper mills, therebyavoiding the additional cost of sending the scrap paper to landfill.

According to a first aspect of the invention, there is provided arelease coating for a pressure sensitive adhesive product comprising:

60-90% polyethylene terephthalate modified by the addition of carboxylfunctional fatty acids and 10-40% water dispersible or emulsifiablesilicone.

According to a second aspect of the invention, there is provided amethod of applying a release coating onto a pressure sensitive adhesiveproduct comprising:

mixing 10-40% water dispersible or emulsifiable silicone with 60-90%polyethylene terephthalate modified by the addition of carboxylfunctional fatty acids in the presence of a suitable catalyst, therebyproducing a release coating; and

applying the release coating to a suitable support.

In other embodiments of the invention, the mixture may be 65-90%modified polyethylene terephthalate and 10-35% water dispersible oremulsifiable silicone.

Polyethylene terephthalate (PET) is used in most plastic beveragebottles. The coatings described herein employ a modified PET that it isdispersible in water so that it can be applied using conventionalcoating equipment as discussed herein. A method for preparing such awater-dispersible PET is described in U.S. Pat. No. 5,858,551 which isincorporated herein by reference in its entirety, particularly thesections describing the preparation of the water-dispersible PET. Themodifications also affect the polymer properties such that it can berepulped when applied to paper packaging.

As discussed in U.S. Pat. No. 5,858,551, the carboxy functional compoundpreferably has at least two carboxyl groups. In preferred embodiments,the carboxy functional compound is selected from the group consisting oftrimellitic acid, trimellitic anhydride, maleic acid, maleic anhydride,fumaric acid and isophthalic acid.

Typical water-based silicone release coatings contain a reactive polymerdispersed in water; this polymer may contain another reactive polymerthat will crosslink with the first polymer or the crosslinking polymermay be incorporated in a second material, for example, a catalyst, whichis added to the reactive polymer prior to usage. The mixture of reactivepolymer, reactive crosslinking polymer and catalyst are typicallyapplied to the paper substrate using a paper coater. The resulting filmis then dried and cured using ovens and/or IR heaters. It is noted thatsuch water-based silicone release coatings are well known in the art.Exemplary examples are described in a number of patents, including butby no means limited to U.S. Pat. No. 5,138,012; U.S. Pat. No. 6,734,217;U.S. Pat. No. 2,606,510; U.S. Pat. No. 2,462,242; U.S. Pat. No.4,448,815; U.S. Pat. No. 4,576,999; U.S. Pat. No. 5,108,782; U.S. Pat.No. 4,423,095 and U.S. Pat. No. 4,454,266.

As will be apparent to one of skill in the art, water based siliconecoatings are preferred within the invention because the water basedsilicone coatings are miscible with the water-dispersible PET describedabove.

Preferably, the water-based silicone release coating is an aqueousemulsion of polyorganosiloxanes and an aqueous emulsion catalyst, forexample, a platinum catalyst. More preferably, the aqueous emulsion ofpolyorganosiloxanes is a mixture of polyorganosiloxanes, water,propylene glycol and polydimethyl (methyl hydrogen) siloxane and theaqueous emulsion catalyst is a mixture of polyorganosiloxanes, water, anemulsifying agent, propylene glycol and a platinum complex.

As noted above, the modified PET is a PET-containing polymer that hasbeen chemically modified with the addition of carboxyl functional fattyacids. Specifically, the modified PET is a water dispersible andredispersible hydrophilic polyester resin derived from PET or recycledPET and has improved hydrophobicity and/or non-polar characteristics, asdescribed in U.S. Pat. No. 5,858,551. As discussed therein, thepolyester resins have a general formula of: I_(n)-P-A_(m) wherein I isthe ionic group, n is an integer of 1-3, P is a polyester backbone, A isan aliphatic group and m is an integer of 3-8. PET content can vary from30-80% though 40-60%, 50-60% or 40-50% is preferred. Due to the carboxylfunctionality on the modified PET, the modified PET is self emulsifyingwhen it is mixed with water that contains a base. Various bases can beused, but ammonia is preferred because it is fugitive; i.e., when thecoating is heated, the ammonia vaporizes leaving a durable surface thatis not easily adhered to by adhesives.

For use, the catalyst is mixed with the silicone water-based coating. Tothis mixture the modified PET is added with agitation in the desiredratio to blend the two materials. This mixture is then applied to apaper surface or other suitable support using similar techniques knownin the art for silicone coatings.

Silicone paper coatings are very expensive; however, by virtue of usinga mixture of silicone and PET, there is a significant reduction in thecost of the release coating. In addition, the coated paper can berepulped and recycled, resulting in a significant income stream to theconverter rather than a cost for sending the material to a landfill.

The instant invention is designed to replace the alternative methodsknown in the art by providing performance to aggressive and standardadhesives while having the added advantage of being repulpable andrecyclable. Adhesive strength is determined by measuring the force inWin required to remove the adhesive backed pressure sensitive label ordecorative top sheet. It is of note that ‘prime’ release is consideredto require 5-15 g/in, ‘medium’ release requires 15-150 g/in while ‘high’release requires 150-500 g/in.

Pressure sensitive adhesives are used in a number of applications. Forexample, they are used in applications such as name tags that utilizeadhesives that are temporary and/or don't have strong adhesivecharacteristics. They can also be used with an adhesive that will haveto permanently bond to the substrate once the protective backing paperis removed. Each application may require a different release surface inorder to maximize performance economically. These categories aretypically known as Repositionable, Reusable or Permanent Labels.

It is known in the industry that the typical coatings (e.g., silicone,chrome complex or PE) that are used in the various applications are notrepulpable or recyclable. The current manufacturers and users have tosend cut waste/matrix from the manufacturing process and used backingpaper to landfill or to an incinerator to dispose of them.

In some embodiments, the modified PET has a recycled plastic content of40-45% and a renewable content (i.e., non-petroleum based) of 20-25%.

A non-recyclable backing paper has a significant cost: the backing paperhas to be sent to landfill or be incinerated; this becomes a cost to theproducer of the backing paper and the user of the final sandwich ofbacking paper, release coating, adhesive and label stock; thisadditional cost will ultimately be reflected in the cost of the endproduct that utilizes the backing paper. If the backing paper can besent back to a recycled paper mill, the producer of the scrap would bepaid for this product.

As will be apparent to one knowledgeable in the art, there are a widerange of adhesives that utilize a release backing paper, depending onthe application. The release coating described herein will provideperformance that will be acceptable from a release perspective for alladhesive classes, but also provide a backing paper that can be repulpedand recycled.

A suitable silicone catalyst is also added. It is noted that suchcatalysts are well known in the art. In a preferred embodiment, thecatalyst is platinum or platinum-based. Exemplary examples of suchcatalysts include but are by no means limited to those described in U.S.Pat. No. 3,159,602; U.S. Pat. No. 3,220,972; European Patent 0,057,459;European Patent 0,188,978; and European Patent 0,190,530.

It has been found that when the modified PET as described above is mixedwith a commercially available water-based silicone release coating basedon rare metal (e.g., platinum complex) addition catalysts as discussedabove, release equivalent to that obtained with silicone, PE or chromecomplex can be achieved when using 10-40% by weight of the silicone (ona dry basis) and 90-60% of the modified PET (on a dry basis). It isbelieved that other silicone cure chemistries will exhibit the sameperformance when utilized with the modified PET described above. Inaddition, these mixtures, unlike the pure silicone, will be repulpableand recyclable.

While not wishing to be bound to a particular hypothesis or theory, itis believed that the fatty acid modified PET orients at the surface ofthe paper so that the fatty acid faces away from the paper providing alow surface energy film to which the adhesive can't adhere. The modifiedPET is compatible with the water-based silicone, as discussed above.

The invention described herein is directed to release backings forvarious pressure sensitive release applications. Pressure sensitiverelease papers are used in a number of applications. These include thesimple and non-demanding applications such as name labels that areindividually removed and applied by an individual. A more demandingapplication would be the labels that are used to attach, for example, aFedEx or UPS label to the box or the plastic covers that are removed toclose the box. The most complex applications are those in which the faceor printed papers are removed by a robot and stuck to a surface. Anexample of this would be medallions and other paraphernalia that areapplied to various consumer products such as autos, appliances and othercommercial items.

As discussed herein, the described coating will perform equally to theprior art silicone coatings but also provide a backing paper that can berecycled and repulped.

In some embodiments, a base coat, for example, a typical pigment (forexample but by no means limited to kaolin clay or other such inorganicmaterial typically used in the paper industry) plus binder (for examplea styrene-butadiene latex) is applied to the surface to be coated priorto the application of the PET/silicone coating. The ratio of pigment tobinder can vary depending on substrate and performance requirements. Inpreferred embodiments, the ratio is between 3:1 and 1:3 pigment to latexsolids.

In use, a commercially available silicone release emulsion and itscatalyst are mixed together in the desired ratios. To this is added aprescribed amount of the modified PET as described above. This mixtureof silicone and PET is then pumped to a coating station where it isapplied to a paper substrate. In some embodiments, depending on thesubstrate, a basecoat such as the one described above is applied to thesubstrate prior to applying the mixture of modified PET and catalyzedsilicone release coating. In some embodiments, the coated paper is driedand cured, for example, such that the coated surface achieves atemperature of about 100C (min); it then must be cooled for example toabout <45C before it is taken to the reel. It is noted that thesetemperatures are intended for illustrative purposes and that othersuitable temperatures will be readily apparent to one of skill in theart through routine experimentation.

This paper is then sent to a converting operation where an adhesive isapplied to the back of a decorative face sheet which is then combinedwith the coated backer sheet. This operation results in some amounts ofscrap paper or cut waste that can now be sent to a recycled mill ratherthan being burned or sent to landfill. As the product approaches the endmarket or ultimate user, waste from the processing or the remainingbacking paper that can recovered from the process can also go to therecycle mill who will pay for this fiber source rather than going tolandfill where the owner will have to pay to have it disposed of.

It is our understanding that typical silicone, QUILON™ (chromecomplex—DuPont) or PE backing papers cannot be recycled. For thesilicone, when recycled they may cause spots on the resulting paperand/or build up on the paper machine. QUILON™ could be a problem becauseof its chromium content; certain oxidative states of chromium are highlytoxic and a paper mill would not want to introduce this potential hazardinto its process. PE laminated backing papers not repulpable; if a PEfilm is used as the backing, it could be recycled into plastic film. Theabove-described PET/silicone combinations are fully repulpable andrecyclable.

While the preferred embodiments of the invention have been describedabove, it will be recognized and understood that various modificationsmay be made therein, and the appended claims are intended to cover allsuch modifications which may fall within the spirit and scope of theinvention.

What is claimed is:
 1. A release coating for a pressure sensitiveadhesive product comprising: 60-90% polyethylene terephthalate modifiedby the addition of carboxyl functional fatty acids and 10-40% waterdispersible or emulsifiable silicone.
 2. The release coating accordingto claim 1 comprising 65-90% modified polyethylene terephthalate and10-35% water dispersible or emulsifiable silicone.
 3. The releasecoating according to claim 1 wherein the carboxyl functional fatty acidis selected from the group consisting of trimellitic acid, trimelliticanhydride, maleic acid, maleic anhydride, fumaric acid and isophthalicacid.
 4. The release coating according to claim 1 wherein the waterdispersible or emulsifiable silicone comprises an aqueous emulsion ofpolyorganosiloxanes and an aqueous emulsion catalyst.
 5. The releasecoating according to claim 4 wherein the aqueous emulsion catalyst is aplatinum catalyst.
 6. The release coating according to claim 4 whereinthe aqueous emulsion of polyorganosiloxanes includes propylene glycoland polydimethyl (methyl hydrogen) siloxane.
 7. The release coatingaccording to claim 4 wherein the aqueous emulsion catalyst comprises anemulsifying agent, propylene glycol and a platinum complex.